Hydrophobic metal oxide particles possess physical properties that are useful in a number of applications requiring a high degree of dispersibility. Some hydrophobic metal oxide particles have physical properties that are desirable for use in toner compositions.
Untreated metal oxide particles are hydrophilic due to the presence of polar groups, such as hydroxyl groups (—OH), on the surface of the untreated silica particles. By treating hydrophilic metal oxide particles, the hydrophilic nature of the particles can be reduced, thereby imparting varying degrees of hydrophobicity to the particles. Many different methods are known for treating the surface of metal oxide particles. However, the direct treatment of an aqueous dispersion of metal oxide particles is often inefficient or difficult to achieve.
Thus, there remains a desire for additional treated metal oxide particles, especially those that are useful for modifying the charge of toner particles, and for additional methods of preparing such hydrophobic metal oxide particles, especially methods that can be used to prepare hydrophobic metal oxide particles directly from an aqueous dispersion. However, not all such particles afford the charge-controlling characteristics that are required for some applications.